COOLANT LEAK

1996 Pontiac Bonneville • 6 cylinder 2WD Automatic • 60,004 miles

1996 Pontiac Bonneville mileage: 60,000. My car has a coolant leak at a gasket under the throttle body assembly. I am told that the gasket and throttle body are a unit and have to be replaced at a cost of approximately $350.00 parts and labor at a Pontiac dealership. Is this a reasonable and correct diagnosis?